Field of the Invention
The invention relates to a packing yarn made from at least two bands that are twisted with one another and are formed of a laminate having layers of two alternately disposed laminar materials which are joined to one another, namely firstly at least one layer of flexible graphite and secondly at least one layer of a reinforcing agent or medium, wherein the reinforcing agent is situated on both outwardly directed flat sides of the flexible graphite of the laminate, or only on one of the outwardly directed flat sides of the flexible graphite of the laminate, or on none of the outwardly directed flat sides of the flexible graphite of the laminate.
An embodiment of that packing yarn includes at least two bands which are joined together by a yarn manufacturing method, e.g. by twisting or braiding, wherein the bands are formed of a laminate composed of a layer of flexible graphite, which is joined at least at one of its two flat sides to a reinforcing agent.
Packing yarns of the type described above are used to manufacture seals and, in particular, packings for sealing shaft and spindle glands. According to a known method, two or more packing yarns are combined for that purpose by using a textile processing method such as, for example, braiding, into a cord or plait. Then portions of such cords or plaits that are cut to a specific, predetermined length are compressed in a suitable pressing mould to form a packing ring. A plurality of such packing rings produce a stuffing-box packing, once they have been inserted into an appropriate packing space of a stuffing-box. According to another known method, portions of a cord or plait made from the packing yarns, which have been cut to length and correspond to the dimensions of a specific packing space, are inserted directly into the gland and the packing that is thus produced, which is still highly compressible, is tightened up by the gland until tightness of the packing configuration is achieved.
According to a third method, the packing yarns or packing cords or plaits manufactured from them may be wound directly around a shaft or spindle having a gland to be sealed, until a quantity of packing yarn or packing plait necessary for producing the required packing has been wound on. Then the winding which is thus produced may, after embedding in the packing space, be tightened up with the aid of the gland until tightness of the packing configuration is achieved.
Packing yarns of the type described above are manufactured i.e. using flexible graphite or expanded graphite. Expanded graphite is obtained by briefly heating graphite salts or intercalation compounds of graphite in the form of an open vermicular material. The flexible graphite is obtained by compressing the expanded graphite which is thus obtained, and is generally produced in the form of graphite foils or graphite plates (see, for example, U.S. Pat. No. 3,404,061). In order to manufacture packing yarns or packing cords or plaits through the use of e.g. braiding, knitting or twisting processes, the graphite foils are cut into strips or bands of a specific width and those strips are then further processed into cords, plaits or strands. Despite a specific flexibility, the strips or bands of flexible graphite tear and/or break during such processing methods because their tensile strength, in particular, is too low. For that reason, a great many possible ways of overcoming the previously mentioned problems associated with manufacturing packing materials from flexible graphite have been indicated.
In one group of solutions to the problem, a substrate of a sufficiently high tensile strength is used, which is finished with a coupling agent, e.g. an adhesive, the substrate is covered with expanded graphite and the expanded graphite and the substrate are pressed together. It is possible to use metal wires, synthetic or natural fibers or yarns, woven fabrics and foils of various types as the substrates. The ropes or bands which are thus obtained are then optionally once more additionally reinforced with yarns, fibers or wires, e.g. by being surrounded by a knitted or braided fabric, or in some other manner and are further processed by using the known processing methods such as braiding into initial products for packings (European Patent Application 0 388 481 A1, corresponding to U.S. Pat. No. 4,961,988; and European Patent 0 466 923 B1, corresponding to U.S. Pat. No. 5,370,405).
In another group of solutions, use is made of graphite foils which have been cut into strips. In that regard, European Patent 0 253 031 B1, which corresponds to U.S. Pat. No. 4,705,722, describes the superimposition of bands of flexible graphite having a width of not more than 5 mm, which are then surrounded by a braided or knitted fabric made from a fibrous material. The strands which are thus obtained are then further braided into plaits, which are suitable as an initial material for the manufacture of packings. According to European Patent 0 466 923 B1, which corresponds to U.S. Pat. No. 5,370,405, graphite foil strips having a width of not more than 5 mm are joined through the use of adhesives to reinforcing organic, inorganic or metal filaments. The reinforced foil strips are processed by braiding, etc. into plaits and the plaits are once more surrounded by a reinforcing fiber braided fabric before being further processed into packings. European Patent Application 0 681 125 A1 discloses the cutting of wide rolls of graphite foils into rolls of reduced width. The foil bands which are thus obtained are provided with a transversely extending embossing or fluting, fluted foil bands are cut into comparatively narrow strips around 2 mm in width, and narrow, fluted strips are combined into a rope and surrounded with a reinforced fiber braided fabric. According to European Patent 0 340 303 B1, which corresponds to U.S. Pat. No. 5,240,769 and U.S. Pat. No. 5,134,030, strips of graphite foil cut to a width of not more than 5 mm are covered with organic, inorganic or metal yarns, fibers or foils and thereby reinforced. Reinforced graphite foil strips are additionally equipped with a further reinforcement of fibers in the course of further processing into braidable or twistable packing yarns.
A plurality of strips of graphite foil may also be superimposed and processed with that technical solution. According to European Patent Application EP 0 794 367 A2, graphite foil bands having a width of more than 6 mm may be reinforced with a plurality of agents, such as wires, bands, yarns of inorganic, metal or organic agents, and then braided into packing cords or plait. There too, the graphite foils may be reinforced by a surface coating of plastic material or by laminating with a plastic material. However, a width of the graphite foil bands, which are provided for braiding or knitting, of more than 5 mm is disadvantageous, as is evident from the disclosures of European Patent EP 0 253 031 B1 or European Patent 0 340 303 B1. Such foils are difficult to process and they produce packing cords of a less dense structure.
For that reason, folding techniques are preferentially used when processing wider bands and layers of graphite foils.
For instance, European Patent Application 0 444 456 A1 teaches that individual foil bands or a plurality of superimposed foil bands are folded at right angles to their longitudinal direction and a packing ring may be obtained from the folded formed body either directly or after the folded formed body has been surrounded by a braided fabric of yarns, fibers or wires. Prior to folding, the foil bands may additionally be combined with yarns, fibers or woven fabrics or such reinforcing agents may be placed between the foil layers prior to folding, for reinforcing purposes. An insertion of corrosion-resistant plastic foils which preferably additionally have sliding properties, such as e.g. polytetrafluoroethylene foils, is also described. However, such plastic foils are not used for reinforcement purposes. According to U.S. Pat. No. 5,605,341 and U.S. Pat. No. 5,549,306, wide graphite foil bands are folded along their longitudinal direction into the shape of an S or a spiral, with it being possible to insert fiber reinforcements prior to or during folding. The strands which are thus obtained are then additionally surrounded by fibers for further reinforcement by braiding or knitting to render them suitable for the manufacture of packings. U.S. Pat. No. 5,225,262 teaches embossing longitudinal profiles in graphite foils and the graphite foils which are thus prepared are folded at least once parallel to the course of the longitudinal profiling. The folded, formed bodies are then surrounded by a yarn, preferably made of INCONEL, using e.g. a braiding or knitting technique, and then calibrated. The strands that are thus produced are then braided into a packing cord, which is calibrated and then once more surrounded by a braided fabric made from a temperature-resistant, high-strength yarn. UK Patent Application GB 2 285 067 A discloses placing graphite foil webs, which may be coated with adhesive, in a plurality of superimposed layers and at least one of the surfaces of such a layered structure is covered with fibers or yarns, which extend parallel to the longitudinal extension of the layered structure and do not cross. The foil layered structures covered with fibers are then cut parallel to the fibers or yarns into strips, and ropes which are thus obtained are folded or rounded in such a way as to produce a strand, that includes a graphite foil core with an outer covering of fibers or yarns running parallel in longitudinal direction. The outer reinforcement with fibers or yarn is intended to prevent wearing-down of the foil graphite when pressure is applied.
European Patent Application 0 601 670 A1 teaches a further method of manufacturing packing yarns or packing bands using graphite foil bands. There, graphite foil bands are initially provided at one of their surfaces with an adhesive layer, to which a yarn with a reinforcing effect is applied.
The graphite foil band provided with the reinforcing yarn is then drawn through a conically tapering nozzle and subsequently pressed flat between two rollers. During that operation, the band is first rounded and then formed, with simultaneous binding-in of the reinforcing yarn and bonding together of the inner-lying surfaces of the graphite foil, into a braidable band which may then be processed into initial products for the manufacture of packings or directly into packings. Application of the adhesive may be effected through the use of a foil which is coated on both sides with adhesive. However, the foil is not used for reinforcement purposes.
In the previously described solutions for manufacturing packing yarns, packing cords, packing bands or packings, either fibers for reinforcing the graphite foils and/or graphite foil bands, which have a low tensile strength, or combinations of fiber reinforcements and foils, are used.
The purposeful application and frictional connection of fibers onto the graphite foil is comparatively difficult and the process of surrounding the outside of graphite foils or graphite foil bands with braided fabric is comparatively costly and in almost every case it is necessary to incorporate at least two reinforcements into the graphite foil bands in order to give them an adequate tensile strength and lend the resulting packing rope good functional properties. When a reinforcement of the graphite foil bands using foils made of different materials is selected, either an additional reinforcement through the use of yarns, fibers or wires or, as in the case of European Patent Application EP 0 794 367 A2, the use of graphite foil bands having a width of 6 mm or more, is necessary.